Sir David Attenborough has defended using footage in his Frozen Planet series of a polar bear tending her newborn cubs that was shot in a zoo.

The veteran broadcaster said the decision to film in the zoo was made for "the safety of the animal".

He told ITV1's This Morning: "If you had tried to put a camera in the wild in a polar bear den, she would either have killed the cub or she would have killed the cameraman, one or the other."

He said explaining about the zoo during the show's commentary would have ruined the atmosphere, adding: "It's not falsehood and we don't keep it secret either".

The BBC has denied misleading viewers over the footage and said the way it had been captured was "clearly explained" in the programme website.

"This particular sequence would be impossible to film in the wild," a spokeswoman said.

"The commentary accompanying the sequence is carefully worded so it doesn't mislead the audience and the way the footage was captured is clearly explained on the programme website."

The footage, narrated by Sir David, was made in a German zoo and was mixed with real wild scenes.

Producer Kathryn Jeffs said on the website that female polar bears give birth at the peak of the winter.

"The problem for us is that they do it underneath the snow in these dens of ice," she said.

"There is absolutely no way that we can get our cameras down there, it would just be completely impractical," she said.

"Even if we could, we would not want to disturb the polar bears by getting that close.

"This was not part of the story that we could leave out of Frozen Planet."

John Whittingdale MP, chairman of the Commons culture, media and sport committee, told the Daily Mirror: "If this was not filmed in the wild it would have been much better to have made that clear in the commentary.

"It's questionable how many people would visit the website and find the video clip which explained the circumstances of the filming."

More than eight million viewers tuned into the episode on November 23.